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An Extinction Map and Color Magnitude Diagram for the Globular Cluster NGC 3201

Abstract

Differential EVβˆ’IE_{V-I} variations of up to ∼0.2\sim 0.2 mag on a scale of arcminutes across NGC 3201 are presented in the form of an extinction map. This map, created by calculating average EVβˆ’IE_{V-I} values for stars in small subregions of the field with respect to a fiducial region, greatly improves the appearance of the CMD of the cluster. We describe how we implemented this technique in detail with our data for NGC 3201. A comparison between our map and that of the same region extracted from the COBE/DIRBE reddening maps published by Schlegel, Finkbeiner, & Davis (1998) (SFD) displays larger-scale similarities between the two maps as well as smaller-scale features which show up in our map but not in the SFD map. Several methods of determining an EVβˆ’IE_{V-I} zeropoint to add to our differential extinction map are presented. Isochrone fitting proved to be the most successful one, but it produces an average EVβˆ’IE_{V-I} for the cluster which is smaller than previously published values by ∼1.5Οƒ\sim 1.5\sigma. Finally, our results seem to support the statement by Arce & Goodman (1999) that the SFD maps overestimate the reddening in regions of high extinction.Comment: 19 pages, 12 figures, 1 table, accepted for publication in AJ (March 2001). Full resolution version may be obtained at http://www.astro.lsa.umich.edu/users/kaspar/html/ngc3201.pdf (PDF) and at http://www.astro.lsa.umich.edu/users/kaspar/html/ngc3201.ps.gz (PS

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    Last time updated on 05/06/2019